1. Field of the Invention
The present invention relates to an apparatus for transferring a testing master block, so called an xe2x80x9cinterim testing artifactxe2x80x9d for inspecting accuracy or checking operation to a measurement table of a three-dimensional measuring machine, so called a xe2x80x9ccoordinate measuring machinexe2x80x9d or other measuring machine.
2. Description of the Related Art
In the past, to measure the dimensions of automobile engines or machine parts such as transmission cases, a measuring machine of the type which measured the dimensions by bringing the front end of a probe into contact with a work piece set on a measurement table has been used widely.
As for this type of measuring machine, there is for example the one disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2-306101. As shown in FIG. 13, the measuring machine A1 has a gantry-type moving member A4 moving in the X-direction along rails A3 at the two sides of the measurement table A2. The moving member A4 has attached to it a moving member A5 able to move in a Y-direction perpendicular to the X-direction.
Further, the moving member A5 is provided with a spindle A5 able to move in the vertical direction, that is, a Z-direction perpendicular to the plane formed by the X-direction and Y-direction. A probe (stylus) A6, to which a ball is affixed, is attached to the front end of the spindle AS. The probe A6 is slid in the X- and Y-directions with the ball in contact with the top surface of the work piece W mounted on the measurement table A2 to detect the dimensions in the Z-direction.
In the measuring machine A1, when the ball at the front end of the probe A6 becomes worn, precise measurement of the dimensions becomes no longer possible, so a V-block is set as a reference gauge on the measurement table A2, the ball is brought into contact with it to detect the dimensions of parts of the V-block, for which error due to the wear of the ball is inspected.
Summarizing the problems to be solved by the present invention, in the measuring machine of the related art disclosed in the Japanese Unexamined Patent Publication (Kokai) No. 2-306101, since the reference gauge is set-by hand on the measurement table between ordinary measurement operations, there was the problem that the inspection of the accuracy of the measuring machine itself required time and trouble due to the set-up work, the ordinary work of measurement of the work piece was suspended for a long time for the inspection of accuracy, and therefore the work efficiency ended up dropping.
Further, to eliminate the trouble of setting the reference gauge at the time of each inspection of accuracy, it is possible to place the reference gauge at a predetermined position on the measurement table at all times and move the probe to the position of the reference gauge for measurement only when inspecting the accuracy, but this means the reference gauge will occupy the space of part of the measurement table at all times, so there was the problem that the location where the work piece could be set on the measurement table ended up becoming limited.
On the other hand, the Japanese Unexamined Patent Publication (Kokai) No. 11-44527 discloses the art of using a conveyor designed for conveying a work piece to a measurement position of a coordinate measuring machine so as to move a testing master block serving as a reference in the accuracy of the dimensions to the measurement position and then measuring the dimensions by the measuring machine. According to this coordinate measuring machine, it is possible to automatically transfer the testing master block to the measurement position and thereby inspect the accuracy quickly.
This coordinate measuring machine, however, has a conveyor attached to convey a work piece mounted on a pallet and the testing master block, so installation of the coordinate measuring machine requires a large space with an enclosed air-conditioning system and temperature control system and therefore there was the problem of a higher capital cost.
An object of the present invention is to provide a transfer apparatus of a testing master block for a measuring machine which enables a testing master block to be transferred onto a measurement table of the measuring machine quickly without human intervention and can be easily attached to an existing measuring machine with a small installation space.
To achieve the above objective, according to the present invention, there is a provided transfer apparatus of a testing master block for a measuring machine provided with a moving member for moving a testing master block for a measuring machine between a retracted position near an end of a measurement table of the measuring machine and a measurement position on the measurement table.
Preferably, the moving member is comprised of a trolley moving between a retracted position set inside a storage housing arranged adjoining an end of the measurement table and a measurement position on the measurement table, and the trolley is provided with a lift mechanism having an elevator frame which is driven to be raised or lowered so as to lift up and hold the testing master block at an ascended position and to lower it onto the measurement table by a descending operation.
More preferably, the storage housing and the trolley are connected through pantograph mechanisms comprised of a plurality of pairs of links, each link of a pair pivotally axially attached to the other at a center position, pivotally connected at their ends to ends of adjoining pairs of links, so as to keep the trolley in line; pairs of nuts formed with female threads in mutually opposite directions to each other are axially attached to be changeable in direction to the ends of the pairs of links positioned at the storage housing side of the pantograph mechanisms; these nuts are engaged with pairs of male threads formed in mutually opposite directions at the outer circumference of a drive screw shaft supported by the storage housing and driven to rotate in both the forward and reverse directions; the pantograph mechanisms extend or contract along with rotation of the drive screw shaft; and thereby the trolley is moved between the retracted position inside the storage housing and the measurement position on the measurement table.
Alternatively, a drive source is mounted on the trolley for driving at least one wheel to propel the trolley between the retracted position in the storage housing and the measurement position on the measurement table, and the storage housing and the trolley are connected by a guide member extendable and contractible in the direction of trolley movement so as to keep the trolley in line.
More preferably, a first positioning means is provided at the bottom of the testing master block, and the first positioning means engages from above with a second positioning means fastened detachably at the measurement position of the measurement table to position the testing master block with respect to the measurement table.
The transfer apparatus of a testing master block for a measuring machine of the present invention (hereinafter referred to simply as a xe2x80x9ctransfer apparatusxe2x80x9d) has a measurement table (bed) for setting a workpiece and can be used attached to a measuring machine for measuring the dimensions etc. of a workpiece placed on that measurement table.
The measuring machine includes for example a coordinate measuring machine which has a probe able to be moved in the X-, Y-, and Z-directions relative to the measurement table and measures dimensions by bringing the front end of the probe into contact with parts of a workpiece on the measurement table.
The transfer apparatus of the present invention moves the testing master block from the retracted position near an end of the measurement table where it does not interfere with ordinary measurement work to the measurement position on the measurement table by a moving member only when inspecting the measuring machine between ordinary measurement operations of workpieces.
Here, as the testing master block, a box-shaped member formed with high accuracy reference holes or reference surfaces for measurement at the surfaces other than the bottom surface may be used. By measuring the testing master block instead of a workpiece, it is possible to inspect the measuring machine for accuracy or malfunctions.
Further, the measuring machine to which the transfer apparatus of the present invention can be applied is not limited to a coordinate measuring machine. It can also be applied to a machine measuring hardness, a machine measuring surface roughness, etc. so long as measurement is performed with the workpiece placed on a measurement table. For example, in the case of a machine measuring hardness, the testing master block becomes a reference master block of hardness, while in the case of a machine measuring surface roughness, the testing master block becomes a reference master block of surface roughness.
Further, the moving member may take various forms such as a trolley able to move on the measurement table carrying a testing master block, a robot arm with a base end attached to a support at the side of the measurement table of the measurement machine and with a front end holding and moving the testing master block to the measurement position on the measurement table, or an extendable fork holding a testing master block at its front end and extending or retracting to move it between the retracted position near an end of the measurement table and the measurement position on the measurement table.
In particular, when using a trolley for the moving member, by making the trolley move between a retracted position set inside the storage housing and the measurement position on the measurement table and storing the testing master block mounted on the trolley inside the storage housing at the retracted position, it is possible protect the high accuracy, expensive testing master block.
Further, by providing the trolley with a lift mechanism having an elevator frame which lifts up and holds the testing master block from the top surface of the measurement table during movement and lowers it on to the measurement table at the measurement position, transfer of the testing master block to the measurement position on the measurement table becomes easy.
Note that the lift mechanism may be configured by a cam mechanism, screw jack mechanism, fluid cylinder mechanism, etc. operating driven by a motor etc.
Further, the opening of the storage housing through which the trolley enters and exits is preferably provided with a shutter which automatically shuts when the trolley enters the retracted position, a cover which may be manually opened or closed, etc. so as to obstruct entry of dust into the storage housing.
Further, the trolley may be moved through pantograph mechanisms by rotation of a drive screw shaft supported at the storage housing by a motor or other rotation source able to drive rotation in both the forward and reverse directions.
In the pantograph mechanisms, by making pairs of nuts, engaged with male threads formed in mutually opposite directions on the drive screw shaft, move in a direction approaching each other or in a direction moving away from each other when the drive screw shaft is rotated, the pairs of links to which these nuts are axially attached at one end pivot about the position of axial attachment between them. This movement is transmitted to all links to make them extend and contract together.
By this extension and contraction of the pantograph mechanisms, it is possible to make the trolley move along a predetermined path between the retracted position inside the storage housing and the measurement position on the measurement table.
Further, it is possible to mount a motor or other drive source on the trolley and drive at least one of the wheels of the trolley by this drive source so as to propel the trolley between the retracted position inside the storage housing and the measurement position on the measurement table.
In this case, by connecting the trolley and the storage housing by a guide member able to extend and contract in the direction of movement of the trolley so as to guide the movement of the trolley, it is possible to keep the trolley in line.
As the guide member, it is possible to use a member configured by combining a plurality of slide rails to be able to expand or contract in the longitudinal direction or pantograph mechanisms comprised of a plurality of pairs of links, each link of a pair pivotally axially attached at its center position with the other link, pivotally connected at their ends with the ends of adjoining pairs of links.
Further, when transferring a testing master block to a measurement position on the measurement table, to eliminate as much as possible the measurement error due to deviation in the orientation of the testing master block etc., it is possible to provide a first positioning means at the bottom of the testing master block and fasten a second positioning means detachably to the measurement position on the measurement table.
In this case, by engaging the first positioning means at the testing master block moved to the measurement position by the trolley of other moving member with the second positioning means on the measurement table from above, it is possible to transfer the testing master block to the measurement position with a high accuracy in two directions in the horizontal plane and in the height direction.
Here, the first positioning means, for example, may be configured by a jig pallet fastened to the bottom of the testing master block formed with conically shaped positioning depressions at three locations on its bottom surface, while the second positioning means may be configured by a reference base provided with steel balls or ceramic balls or other spherical members or conically shaped projections at positions matching with the conically shaped positioning depressions.
Note that the reference base may be bolted etc. to a T-slot etc. formed for attachment of the jigs etc. to the measurement table of the measuring machine.
Further, instead of the conically shaped positioning depressions, it is possible to form a plurality of elongated positioning holes having widths matching the diameters of the spherical members in the bottom surface of the jig pallet so as to extend in two different directions in the plane parallel to the top surface of the measurement table. Alternatively, it is possible to provide spherical members at the jig pallet side of the testing master block and form positioning depressions or elongated positioning holes in the reference base.
Further, it is possible not to fasten the jig pallet to the bottom of the testing master block, but to directly form positioning depressions or elongated holes in the bottom surface of the testing master block and use the positioning depressions or elongated holes themselves as the first positioning means.
Further, the first positioning means and the second positioning means may be configured using a plurality of groups of knife edges and V-grooves engaging with each other so as to position the testing master block in a plurality of different directions parallel to the top surface of the measurement table and in the height direction.